What is required to stabilize Al3+? A gas-phase perspective.

With a combination of experiment and theory (ab initio and DFT), we demonstrate that the Al(3+) cation can be stabilized in the gas phase using ligands, which have the ability to act as powerful sigma electron donors and electron acceptors. The latter property, which implies that electron density from the aluminum cation moves into ligand antibonding orbitals, has not previously been considered significant when accounting for the behavior of Al(3+). Of the three ligands identified as falling into the above category, acetonitrile appears to form the most stable complexes in the gas phase, which is in accord with the long established fact that solid-state complexes with Al(3+) are readily isolated. From the results, it is suggested that chain or ring compounds containing the -C triple bond N group might act as successful sequestering agents for Al(3+) from aqueous solutions.